Your argument about lifespan doesn't seem to make sense. Every species has some lifespan. Many are shorter than dairy cows. How do you decide what the "proper" lifespan is? Is it the lifespan of its ancestors? How many generations back do you go? Go too far and it may become shorter again. At the end of the day, a cow doesn't worry "oh I'm only going to live 4 years instead of the 20 that those lucky wild cows used to have".

I think you're invoking a human emotion about dying and having a short life which is entirely meaningless in the context of cows.